The invention relates generally to the field of computer graphics and image manipulation, and in particular to techniques for generating intermediate images from a plurality of original images.
The ability to generate a large number of images of an environment from closely spaced viewpoints is used in traditional virtual reality applications. A typical virtual reality application is a walk through a virtual environment, such as is offered in some web-based applications to allow potential home buyers to walk through the virtual home environments of homes that are offered for sale. Many other applications are well known in this art. In many of these cases, the same scene is displayed from a viewpoint controlled by the user. Consequently, a different view of a scene must be determined and presented for each different location of the viewpoint. Ordinarily, a computer is used to repetitively render the scene from the different viewpoints.
In U.S. Pat. No. 5,613,048, entitled xe2x80x9cThree-dimensional Image Synthesis using View Interpolationxe2x80x9d, which issued Mar. 18, 1997 to Chen et al., three-dimensional scenes are portrayed from different viewpoints by morphing two-dimensional images. Image morphing deals with the metamorphosis of an image to another image. The metamorphosis generates a sequence of intermediate images in which an image gradually changes into another image over time. In Chen et al., various key views of an image are stored, along with offset maps that identify the correspondence of pixels in adjacent stored images. When an intermediate view of the scene is to be presented, one or more stored views are interpolated through a morphing technique.
In such systems, the stored images can be computer-generated images, artist""s renditions and/or digitized versions of respective photographic images. The scene can then be viewed from any viewpoint within a continuous range defined by the stored images, providing a more realistic presentation. Generally speaking, the greater the number of actual images that are stored from the various viewpoints, the more realistic the presentation may become.
Full 360 degree panoramic images are a means of producing visual content for a wide variety of applications, including virtual reality applications. There are a large number of well known methods to produce such images, and the capability has been available for many years. Panoramic images have typically been acquired by expensive and specialized camera systems, such as the RoundShot cameras offered by Seitz Phototechnik AG of Lustdorf, Switzerland. These special cameras rotate around their own axis during exposure and capture a true 360 degree panoramic image. Through the widespread use and availability of digital imaging, the requirement for specialized cameras has been relaxed, and panoramic images can instead be composed from a collection of standard images. Instead of a camera that captures a panoramic image directly into a single image, a series of standard images are recorded by an ordinary digital or film camera and later combined into a panoramic image. The distinguishing feature of the collection of images is that each image is recorded with the camera pointing in a different horizontal direction.
One attractive feature of digital panoramic images is that the viewer can be given the freedom to select the view angle and the amount of zoom. This freedom to explore the image from selected view angles is an aspect of what is sometimes referred to as virtual reality. However, the image is in fact a two-dimensional image and the viewer""s spatial position is not allowed to change; only the angular viewing directions may change. Another way to consider this is to remember that a viewer has six degrees of freedom: three spatial, two angular and one zoom degrees of freedom. The traditional panoramic imaging systems at most grant the viewer freedom only with three of the degrees of freedom, that is, only with two angular and one zoom degrees of freedom.
Traditional suites of software, such as the BeHere system provided by BeHere Corp and the iPix(copyright) 360 Suite provided by Internet Pictures Corp., allow a viewer to experience different views within a 360 degree field of vision. The BeHere system utilizes an actual 360xc2x0 image generated by a stationary panoramic imaging arrangement, such as the one described in their U.S. Pat. No. 6,175,454, entitled xe2x80x9cPanoramic Imaging Arrangementxe2x80x9d, which issued Jan. 16, 2001 to Hoogland et al. The iPix(copyright) 360 Suite creates immersive images by combining two 185xc2x0 film or digital photographs taken with a fisheye lens into one 360xc2x0 by 360xc2x0 spherical image. In applications such as the aforementioned xe2x80x9cvirtual-walk-throughsxe2x80x9d, which may be produced by the iPix(copyright) 360 Suite and the BeHere system (among others), the viewer is often given an ensemble of virtual images and is permitted to move from one panoramic image to another. However, the transition between successive panoramic images is abrupt, as there are no spatial degrees of freedom.
A similar situation exists for two images of the same object or scene taken from different vantage points. The transition between the two images is abrupt. Image morphing techniques can generate compelling two-dimensional transitions between the images. However, differences in object pose or viewpoint often cause unnatural distortions in image morphs that are difficult to correct manually. It is possible, however, through a technique known as View Morphing, (see S. Sietz, and C. Dyer, xe2x80x9cView Morphing,xe2x80x9d Proceedings of SIGGRAPH 1996) to produce a series of intermediate two-dimensional images that give the viewer the sensation of moving between the two views. Using basic principles of projective geometry, view morphing introduces a extension to image morphing that correctly handles three-dimensional projective camera and scene transformations. This technique works by prewarping two images prior to computing a morph and then postwarping the interpolated images. Because no knowledge of three-dimensional shape is required, the technique may be applied to photographs and drawings, as well as rendered scenes. The ability to synthesize changes both in viewpoint and image structure affords a wide variety of interesting three-dimensional effects via simple image transformations. The result is quite startling, as the method appears to convert two still photographs into a series of movie frames. Hence, a different degree of freedom is granted to the viewer.
Generating an intermediate image from two images using view morphing, involves the following steps: (1) identifying correspondence points between the two images (manually or automatically), (2) determining the epipolar geometry (by estimating the fundamental matrix), (3) pre-warping the two images, (4) morphing the pre-warped images to form an intermediate warped image, and (5) post-warping the intermediate warped image. In some instances (such as when the two viewpoints are similar), the pre- and post-warping steps (3) and (5) can be omitted in the interest of execution speed.
The foregoing techniques have been successfully applied to the creation of intermediate images where the transition is between original planar images. The approach taken in panoramic imaging, however, is to treat the viewer to an immersive view from a given viewpoint within a captured, original panoramic image. The lack of planar images hinders the generation of intermediate images. Nonetheless, it would be useful, particularly in virtual imaging applications, to extend the techniques of intermediate imaging to panoramic imaging.
The present invention is directed to overcoming one or more of the problems set forth above. Briefly summarized, according to one aspect of the present invention, a method for generating an intermediate panoramic image from two original panoramic images, where each panoramic image provides a 360 degree field of view of a scene from different nodal points, comprises the steps of: (a) generating pairs of planar images corresponding to original planar views derived from respective portions of the original panoramic images, whereby a similar area of the scene is visible from each pair of planar views; (b) generating an intermediate planar image from each pair of planar images, thereby generating a series of intermediate planar images; and (c) generating an intermediate panoramic image from the cylindrical concatenation of the intermediate planar images.
These and other aspects, objects, features and advantages of the present invention will be more clearly understood and appreciated from a review of the following detailed description of the preferred embodiments and appended claims, and by reference to the accompanying drawings.